Understanding mycobacterial protective immunity in the murine model

Project Overview

Tuberculosis (TB) is the deadliest infectious disease with 10.4 million new cases and 1.8 million deaths in 2015. It is estimated that currently one third of the world’s population is infected with TB. Bacillus Calmette Guerin (BCG) is the only currently available vaccine and although protective against childhood forms of TB, its efficacy is highly variable in adults, a population that is responsible for the majority of disease burden. An effective vaccine that targets this population would prevent and reduce disease.

Challenging humans with Mycobacterium tuberculosis (M.tb) is unethical and therefore testing new vaccines requires the use of animal models, although the relevance of these animal models is not yet clear. The McShane group are exploring an alternative strategy that exploits the similarity between M.tb and BCG. In an on-going human experimental medicine study, healthy volunteers inhale aerosolised BCG, as a surrogate for M.tb infection. Lung washing and blood samples are then taken at different timepoints ‘post-infection’ to assess immune responses. These data will give invaluable insights into the intricate balance between mycobacterial infection and mycobacterial containment by the human host. In addition, it could lead to a new way to test the efficacy of vaccine candidates in humans. The proposed PhD project described here aims to replicate the above study in the mouse model of M.tb infection. The mouse model is one of the most important animals models to evaluate vaccine candidates as they can be infected with M.tb. However it is not known how well this model represents human infection.

This PhD project will critically allow parallel human and murine studies which will allow important connections to be made between the human and mouse model. It involve a wide range of techniques ranging from immunisations, M.tb infections using state of the art aerosolised machine in Biosafety level 3 laboratories, cellular and humoral immunology and molecular biology.

Training Opportunities

A broad range of training opportunities will be provided. These range from lab-specific techniques’ such as: working safely in BSL3 laboratories, animal handling and immunizations, a huge array of immunological assays such as flow cytometry, cell sorting, ELISPOTS and molecular biology techniques. In addition, more generic training will be provided in analyzing and plotting data, thesis writing and presentation courses. The McShane group has 17 years experience in TB vaccine development and immunology and a very experienced clinical and research team.

BACKGROUND: Intradermal MVA85A, a candidate vaccine against tuberculosis, induces high amounts of Ag85A-specific CD4 T cells in adults who have already received the BCG vaccine, but aerosol delivery of this vaccine might offer immunological and logistical advantages. We did a phase 1 double-blind trial to compare the safety and immunogenicity of aerosol-administered and intradermally administered MVA85A METHODS: In this phase 1, double-blind, proof-of-concept trial, 24 eligible BCG-vaccinated healthy UK adults were randomly allocated (1:1) by sequentially numbered, sealed, opaque envelopes into two groups: aerosol MVA85A and intradermal saline placebo or intradermal MVA85A and aerosol saline placebo. Participants, the bronchoscopist, and immunologists were masked to treatment assignment. The primary outcome was safety, assessed by the frequency and severity of vaccine-related local and systemic adverse events. The secondary outcome was immunogenicity assessed with laboratory markers of cell-mediated immunity in blood and bronchoalveolar lavage samples. Safety and immunogenicity were assessed for 24 weeks after vaccination. Immunogenicity to both insert Ag85A and vector modified vaccinia virus Ankara (MVA) was assessed by ex-vivo interferon-γ ELISpot and serum ELISAs. Since all participants were randomised and vaccinated according to protocol, our analyses were per protocol. This trial is registered with ClinicalTrials.gov, number NCT01497769. FINDINGS: Both administration routes were well tolerated and immunogenic. Respiratory adverse events were rare and mild. Intradermal MVA85A was associated with expected mild local injection-site reactions. Systemic adverse events did not differ significantly between the two groups. Three participants in each group had no vaccine-related systemic adverse events; fatigue (11/24 [46%]) and headache (10/24 [42%]) were the most frequently reported symptoms. Ag85A-specific systemic responses were similar across groups. Ag85A-specific CD4 T cells were detected in bronchoalveolar lavage cells from both groups and responses were higher in the aerosol group than in the intradermal group. MVA-specific cellular responses were detected in both groups, whereas serum antibodies to MVA were only detectable after intradermal administration of the vaccine. INTERPRETATION: Further clinical trials assessing the aerosol route of vaccine delivery are merited for tuberculosis and other respiratory pathogens. FUNDING: The Wellcome Trust and Oxford Radcliffe Hospitals Biomedical Research Centre. Hide abstract